Aluminum base alloys



Patented Jan. 10, 1939 UNITED STATES PATENT OFFICE ALUMINUM BASE ALLOYS London, England No Drawing. Application June 29, 1937, Serial No. 151,038. In Great Britain July 8, 1936 1 Claim.

This invention relates to certain types of aluminum alloy, viz. the known aluminum copper and aluminum copper zinc 'alloys such as may be used for rolling into sheet, and containing up to 5 12 per cent. by weight of copper with or without tin up to 2 per cent. by weight.

It is known that certain aluminum alloys when hardened by ageing, heat treatmentiollowed by artificial ageing or cold working, give a product 0 of very fine finish when machined. The turning of such alloys on automatic or turret lathes presents a difficulty in that theyare not freecutting, that is the curling of the cuttings fouls the tools and makes their removal by means of the 15 tool coolant almost an impossibility.

The addition of tin assists in producing a freecutting condition in certain aluminum base alloys, but it is difficult to hot-work such alloys by rolling, pressing or extrusion on account of hotshortness.

The object of the present invention is to produce an aluminum base alloy of the above class which may be successfully hot-worked, may be machined to a very fine finish and which is freecutting, that is, the short chips or cuttings produced by machining do not foul the cutting tool or are not difiicult to remove.

I have found that the admixture of antimony in the manner and proportions hereinafter described with the above described aluminum base alloys will produce alloys fulfilling the above objects and that the finish of the antimony containing alloys is improved when tin is used as an ingredient.

The following are examples of alloys which, when prepared by the procedure given below, are capable of being freely cut to a high machine finish after having been hot-worked at .a temperature in the neighborhood of 500 C. and allowed to cool in air.

Composition EXAMPLE I Parts by weight Copper 3.0 Magnesium 0.5 Tin 0.24 Antimony 0.44 0 Aluminum to complete 100 ExAmgLr: II

Copper 3.0 Magnesium 0.5 Antimony 1.21

Aluminum to complete 100 EXAMPLE III Parts by weight Copper 1.0-12.0 Magnesium 0. 0.5 Tin 0.1- 2.0 Antimony 0.1- 5.0 Aluminum to complete I EXAMPLE IV Copper 1.0-l2.0 Magnesium 0. 0.5 Antimony 0.1- 5.0 Aluminum to complete 100 EXAMPLE V Copper 1.0- 6.0 Zinc 8.0-20.0 Magnesium 0. 0.5 Tin 0.1- 2.0 Antimony 0.1- 5.0 Aluminum to complete 100 EXAMPLE VI Copper 1.0 6.0 Zinc 8.0-20.0 Magnesium 0. 0.5 Antimony 0.1- 5.0 Aluminum to complete 100 Procedure In all the above cases the antimony is melted with any convenient weight of aluminum, for example, 50% of the aluminum content, and the mixture held at a temperature of about 920 C. and for about 45 minutes to form a hardener alloy in which no free antimony exists.

The presence or otherwise of free antimony may be determined for instance by the examination of micro-sections at about 300 magnifications.

This method shows free antimony as small dark areas intermingled with a network of aluminumantimony compound (half-tone) on the light background of primary aluminLun. If the hardener alloy has been correctly produced, .the dark areas referred-to above are absent and the field consists entirely of a network of aluminumantimony (half-tone) on the lighter background of primary aluminum.

The hardening mixture is then added to the remaining ingredients of the alloy whilst the latter are in a molten condition.

General The proportion of antimony in the case of tin containing alloys is preferably greater than that of tin, the antimony content not exceeding 5.0

per cent. and the tin content not exceeding 2.0 per cent. and in order to ensure that the tin-antimony compound is equally distributed throughout the mass and in the required proportion,'a hardener alloy of aluminum plus an aluminum-antimony compound is prepared, by holding at an elevated temperature for a considerable time a mixture of aluminum and antimony. This hardening mixture is then added, in correct proportion, to the molten aluminum base alloy to which tin has already been added.

I claim:

A hot workable, hardenable aluminum base alloy capable of taking a very fine flnish and which is at the same time free cutting and which contains from 1 to 6 per cent, by weight of copper, 0.1 to 5.0 per cent. by weight of antimony, an eflective amount to 0.5 per cent. by weight oi magnesium, the remainder being substantially all aluminum.

JAMES HERBERT DICKIN. 

